The present invention relates to photosensitive members having a photosensitive layer containing distyryl compounds.
In electrophotography generally known are a direct process in which electrostatic charge and exposure are applied onto the surface of photosensitive layer of a photosensitive member to form an electrostatic latent image which is then visualized by development with a developer and the visual image is fixed directly as it is on the photosensitive member to obtain a copied image; the particle figure transfer process in which visual images on a photosensitive member are transferred to paper or other materials and the transferred images are fixed to obtain copied images; and a latent image transfer process in which electrostatic latent images on a photosensitive member are transferred onto transfer paper and the electrostatic latent images on the transfer paper are developed and fixed.
As the materials employed for the construction of the photosensitive layer of the photosensitive member in these types of electrophotographic process, selenium, cadmium sulfide, zinc oxide and other inorganic photoconductive substances are known.
While these photoconductive substances have many profitable features as, for example, they allow only little dissipation of charge in the dark and dissipate charge rapidly upon exposure of light, they have various disadvantages. For example, the selenium-type photosensitive members require difficult manufacturing conditions and high manufacturing costs and special care for handling because they are fragile to heat and mechanical impacts. The cadmium sulfide-type and zinc oxide-type photosensitive members are so defective that stable sensitivity is hardly obtained in humid environment and stable capacity over a long period cannot be expected because the pigment added as a sensitizer causes deterioration in electrostatic charge due to corona electrical charging and photodiscoloration due to exposure.
On the other hand, various organic photoconductive polymers including polyvinylcarbazole have been proposed but while these polymers are superior to the above inorganic materials in layer formation, light weight and other properties they are still inferior to the inorganic substances in regard to achieving sufficient sensitivity, durability and stability in changing environment.
In the case of organic photoconductive compounds with low molecular weights, it is profitable to be able to control the physical properties or electrophotographic characteristics of the coated layer by selecting the kind and composition ratio of the binder to be used together, but the combination of the organic photoconductive material with a binder resin requires high compatibility of the compounds with the binder.
The photosensitive members made by dispersing such organic photoconductive compounds of high or low molecular weight are defective in that they show high residual potential and low sensitivity due to much trapping of carrier. Therefore it has been proposed to formulate a charge-transporting material to the photoconductive compounds to overcome these defects.
Also the separated function-type photosensitive members have been proposed in which the charge-generating function and the charge-transporting function of the photoconductive function are divided to different substances. In such a type of photosensitive members, a number of organic compounds have been considered as the charge-transporting materials to be used in the charge-transporting layer, but they bring about many problems. For example, 2,5-bis(p-diphenylaminophenyl)1,3,4-oxadiazole which is reported in U.S. Pat. No. 3,189,447 has so low a compatibility with binders that it is readily crystallized out. The diarylalkane derivatives described in U.S. Pat. No. 3,820,989 have good compatibility with binders but show change in sensitivity when used repeatedly. The hydrazone derivatives described in Japanese Patent Laid-Open Publication No. 59143/1979 show relatively good characteristics of residual potential but have such shortcomings as poor capacity for electrostatic charge and repeatability.
Thus, it is concluded that few organic compounds of low molecular weight with practically satisfactory characteristics for making photosensitive members are known presently.
It should be noted that distyryl compounds were disclosed as the compounds with good charge-transporting ability in Japanese Patent Laid-Open Publications Sho-60 175052 and Sho-62 120346, but they are quite different in chemical structure from the compounds to be disclosed in the present application.